Project summary Parasitic nematodes impose a massive health and economic burden across much of the developing world, infecting over one billion humans worldwide and conservatively resulting in the loss of 14 million disability- adjusted life years (DALYs) per annum. The morbidity and mortality inflicted by these devastating pathogens is partly curtailed by well-organized mass drug administration (MDA) programs that depend on the continued efficacy of a limited portfolio of anthelmintic drugs. Avermectins are a widely used (and recently lauded) class of broad-spectrum anthelmintics that are an indispensable component of this limited chemotherapeutic arsenal. The human-approved avermectin formulation, ivermectin, is a mainstay in the treatment of many parasitic nematode infections such as Lymphatic Filariasis (LF) and is considered an `Essential Medicine' by the WHO. The prospects of avermectin resistance pose a serious threat to the future success of nematode control programs. These prospects have been realized in the veterinary domain following intensive avermectin use, and are predicted to materialize in human medicine with increased selection pressures resulting from expanded MDA coverage. Early detection of avermectin resistance-associated alleles in nematode parasite populations is essential to the goal of slowing anthelmintic resistance and extending the lifespan of this critical drug class. Despite consensus on urgency, very little is known about the genetic and molecular determinants of avermectin resistance. The experimental intractability of human nematode parasites necessitates the development of new approaches to discover and validate relevant markers for resistance. We propose to utilize the powerful model nematode Caenorhabditis elegans to systematically interrogate the complex genetic determinants of avermectin resistance. This model was crucial towards understanding anthelmintic resistance in parasites, including identification of glutamate-gated chloride channels as the target of avermectins. Our central hypothesis is that C. elegans can be used to identify genetic loci that are predictive of avermectin resistance in medically important human parasites. To establish mechanistic conservation, putative genetic markers identified in C. elegans will be validated experimentally in the vector-borne human filarial parasite Brugia malayi, an etiological agent of LF. Upon completion, this project will make available a new statistical genetics toolkit and molecular pipeline for the discovery and validation of parasite-relevant anthelmintic resistance mechanisms.